Remove uses of Path class from tests/standalone.

tests/standalone/io/http_proxy_test.dart

Index: tests/standalone/io/http_proxy_test.dart
diff --git a/tests/standalone/io/http_proxy_test.dart b/tests/standalone/io/http_proxy_test.dart
index 70e06b651e7d61d3bca947373480a3de7087e0ea..3b56004e08fe39d606526f135c39a35bf3b24189 100644
--- a/tests/standalone/io/http_proxy_test.dart
+++ b/tests/standalone/io/http_proxy_test.dart
@@ -4,6 +4,7 @@
 
 import "package:crypto/crypto.dart";
 import "package:expect/expect.dart";
+import "package:path/path.dart";
 import "dart:async";
 import "dart:io";
 import 'dart:utf';
@@ -745,9 +746,8 @@ void testRealProxyAuth() {
 }
 
 void InitializeSSL() {
-  var testPkcertDatabase =
-      new Path(Platform.script).directoryPath.append('pkcert/');
-  SecureSocket.initialize(database: testPkcertDatabase.toNativePath(),
+  var testPkcertDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: testPkcertDatabase,
                           password: 'dartdart');
 }